Method and apparatus for measuring the size of free air balls on a wire bonder

ABSTRACT

A system for measuring the size of free air balls for use with a wire bonder having a wire bonding tool and an Electric Flame Off (EFO) device is provided. The system includes an imager disposed above a first image plane, a prism disposed below the imager, and at least one lens positioned between the first image plane and the prism in a first optical path. The at least one lens is positioned between the prism and the imager in a second optical path, where the second optical path is different from the first optical path. An image of the free air ball disposed at a lower portion of the wire bonding tool is provided to the imager via the prism and the at least one lens.

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 60/581,575, filed on Jun. 21, 2004, the contentsof which are incorporated in this application by reference. Thisapplication is a continuation-in-part of U.S. patent application Ser.No. 10/458,535, filed on Jun. 10, 2003 now U.S. Pat. No. 6,997,368 whichis a divisional of U.S. patent application Ser. No. 10/131,873, filed onApr. 25, 2002, issued as U.S. Pat. No. 6,729,530 on May 4, 2004, whichis a continuation-in-part of U.S. patent application Ser. No. 09/912,024filed on Jul. 24, 2001, issued as U.S. Pat. No. 6,412,683 on Jul. 2,2002.

FIELD OF THE INVENTION

The invention relates generally to a method and apparatus for measuringthe size of free air balls on a wire bonder. More specifically, thepresent invention relates to the use of a prism such as a cornercubeprism to produce the image of a capillary tip with a free air ballpresent. The present invention is used in conjunction with a machinevision system to analyze the image and measure the diameter of the ballprior to bonding.

BACKGROUND OF THE INVENTION

The fabrication of electronic assemblies, such as integrated circuitchips, typically involves inspection of the device at various phases ofthe fabrication process. Such inspection procedures often utilize visionsystems or image processing systems (e.g., systems that capture images,digitize them and use a computer to perform image analysis) to guide thefabrication machine for correct placement and/or alignment ofcomponents.

In fabricating such electronic assemblies, wire bonding is typicallyused to interconnect the integrated circuit chip with a lead frame.Other well-known interconnect processes include, for example,ball-bumping and stud-bumping. As part of these bonding processes abonding ball is formed at the end of the bonding wire using a well-knownelectric flame-off (EFO) technique. The size (diameter) of the bondingball (free air ball) depends on the current and duration of the EFO. Aswire bonders are used for packaging finer and finer pitch devices, itwould be desirable to measure and control free air ball diameters in aneffort to regulate ball size for ultra fine pitch application.

A conventional vision system (shown in FIG. 11) consists of two imagedevices, a first image device 1104 placed below workpiece plane 1112 andupwardly viewing objects and a second image device 1102 placed aboveworkpiece plane 1112 and downwardly viewing objects. These conventionalsystems have drawbacks in that in addition to requiring more than oneimage device, they are unable to easily compensate for variations in thesystem due to thermal changes, for example.

Further, in conventional systems, bonding ball diameter is typicallymeasured off-line. That is, the bonding process is interrupted so thatthe ball diameter or the resultant stud (in the case of stud-bumping)can be measured. Changes in the size of the bonding ball are then madeto the EFO system, again off-line, to correct for the size of thebonding ball. Thus, the bonding ball size is measured and adjusted viaan off-line calibration sequence and programmed into the wire bonder.

These conventional systems have deficiencies, however, in that they haveno way of determining the effect of these settings without again goingto an off-line measurement. Thus, the ball size determination andcontrol is open loop and requires interrupting the bonding process,negatively impacting device throughput.

Accordingly, it would be desirable to provide a system and method forallowing a wire bonder to periodically measure the ball diameter so thatthe EFO system may be controlled to produce the desired size ballcontinuously without the necessity to interrupt the ball bonding processwith off-line measurements and adjustments.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a systemfor measuring the size of free air balls for use with a wire bonderhaving a wire bonding tool and an Electric Flame Off (EFO) device isprovided. The system includes an imager disposed above a first imageplane, a prism disposed below the imager, and at least one lenspositioned between the first image plane and the prism in a firstoptical path. The at least one lens is positioned between the prism andthe imager in a second optical path, where the second optical path isdifferent from the first optical path. An image of the free air balldisposed at a lower portion of the wire bonding tool is provided to theimager via the prism and the at least one lens.

According to another exemplary embodiment of the present invention, amethod for measuring a size of a free air ball for use with a wirebonder having a wire bonding tool and an Electric Flame Off (EFO) deviceis provided. The method includes receiving an indirect image of the freeair ball via a prism, processing the received image of the free air ballto measure at least one dimension of the free air ball, and providing acontrol signal to the EFO device based on the at least one dimension ofthe free air ball.

According to yet another exemplary embodiment of the present invention,a method for analyzing an image of a free air ball for use with a wirebonder having an Electric Flame Off (EFO) device is provided. The methodincludes providing an image of the free air ball to an image processorduring a wire bonding process, determining whether a characteristic ofthe free air ball is within a predetermined tolerance, and controllingat least one setting of the EFO system based on the determination step.

These and other aspects of the invention are set forth below withreference to the drawings and the description of exemplary embodimentsof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following Figures:

FIG. 1 is a perspective view of an exemplary embodiment of the presentinvention;

FIG. 2A is a side view of image ray traces according to a firstexemplary embodiment of the present invention;

FIG. 2B is a side view of image ray traces according to a secondexemplary embodiment of the present invention;

FIG. 3 is a perspective view of image ray traces according to anexemplary embodiment of the present invention;

FIGS. 4A and 4B are perspective and side views, respectively, of anexemplary embodiment of the present invention;

FIG. 5 illustrates the telecentricity of an exemplary embodiment of thepresent invention;

FIG. 6 is a detailed view of an exemplary retroreflective cornercubeoffset tool according to the present invention;

FIGS. 7A-7C illustrate the effect of tilt about the vertex of thecornercube tool of the exemplary vision system;

FIGS. 8A-8C illustrate the effect of tilt about the X and Y axis of theexemplary vision system;

FIG. 9 is a side view of image ray traces according to a third exemplaryembodiment of the present invention;

FIGS. 10A-10D are various views of a fourth exemplary embodiment of thepresent invention;

FIG. 11 is a vision system according to the prior art;

FIG. 12A-12F are illustrations of a fifth exemplary embodiment of thepresent invention;

FIGS. 13A-13D are various views of a sixth exemplary embodiment of thepresent invention;

FIG. 14 is a side view illustrating an apparatus for measuring free airballs with a wire bonder optical system according to an exemplaryembodiment of the present invention; and

FIG. 15 is a schematic block diagram of an exemplary apparatus formeasuring and adjusting free air balls with a wire bonder opticalsystem.

DETAILED DESCRIPTION

The entire disclosure of U.S. patent application Ser. No. 10/458,535filed on Jun. 6, 2003 and U.S. patent application Ser. No. 09/912,024filed on Jul. 24, 2001 are expressly incorporated by reference herein,as if set forth in full.

According to certain exemplary embodiments, the present inventionrelates to a method and apparatus for measuring the size of a free airball on the optical system of a wire bonder along with an opticalcornercube prism based technology to image the capillary tip.

According to certain exemplary embodiments thereof, the presentinvention uses the optical system of a wire bonder and a cornercubebased offset tool to image the free air ball disposed adjacent to orseated in the wire bonder capillary. The image is then analyzed tomeasure the ball size. To improve the accuracy of the ball measurement,an illumination system appropriate for producing a desirable image(e.g., high magnification image) is utilized. The optical system may beselected to produce the desired image (e.g., a low magnification image,a high magnification image, or any appropriate resolution, etc.) basedon a number of factors including, for example, the size of the free airball and other processing constraints. The system measures the diameterof a ball during normal operation of a wire bonder. The information isused to control the ball size via the EFO ball formation mechanismcommonly found on wire bonders. The purpose of the system is to measurefree air ball diameter in an effort to regulate the ball size for ultrafine pitch applications. The wire bonder then uses these values todetermine and adjust settings for the EFO system.

According to another exemplary aspect of the invention, the ball sizedetermination and control is a closed loop process. The wire bonderperiodically measures the ball diameter and provides this information tothe wire bonder so that the EFO system may produce the desired ball sizecontinuously. This allows the free air ball size to be controlled duringbonding operations, therefore correcting for any disturbances whichwould cause a free air ball to exceed its desired diameter toleranceduring a wire bonding operation.

Currently, no apparatus or method exists on the wire bonder formeasuring free air balls. According to certain exemplary embodimentsthereof, the present invention allows the free air ball size to becontrolled in a closed loop manner and therefore correct for anydisturbances which would cause the free air ball to exceed its desireddiameter tolerance during wire bonding operation.

The present invention allows the wire bonder to periodically measure theball diameter and provide this information to the wire bonder so thatthe EFO system may produce the desired size ball continuously. A machinevision system may be used to analyze the image and measure the balldiameter. The present invention uses this information to control theball size via the EFO ball formation mechanism commonly found on wirebonders today.

Referring to FIG. 1, a perspective view of an exemplary embodiment ofthe present invention is shown. The system is included in wire bondingmachine 100, and employs a cornercube 106 (i.e., a cornercube prism106), having a plurality of internal reflection surfaces (best shown inFIG. 6), located at or below object plane 112A of bonding tool 104(object plane 112A, shown in FIG. 2A, is part of plane 112 illustratedin FIG. 1).

In an exemplary embodiment, cornercube offset alignment tool 109(comprising cornercube 106 and lens elements 108, 110), has a total ofthree internal reflection surfaces, 218, 220, and 221 (best shown inFIG. 6 and described below). In another exemplary embodiment, cornercube106 may have a plurality of total internal reflective surfaces. Forexample, cornercube 106 may be formed from or include fused silica,sapphire, diamond, calcium fluoride or other optical glass. Note,optical quality glass, such as BK7 made by Schott Glass Technologies ofDuryea, Pa., may also be used. Note also that materials for cornercube106 can be selected for maximum transmission with respect to the desiredoperating wavelength.

Optical imaging unit 102, such as a CCD imager, CMOS imager or a camera,for example, is mounted above image plane 112B in order to receive anindirect image of bonding tool 104 through cornercube offset alignmenttool 109 (image plane 112B, shown in FIG. 2A, is part of plane 112illustrated in FIG. 1). In another exemplary embodiment, a positionsensitive detector (PSD), such as that manufactured by Ionwerks Inc., ofHouston, Tex., may also be used as optical imaging unit 102. In such anembodiment, when the hole in bonding tool 104 is illuminated, such as byusing an optical fiber for example, the PSD can be utilized to recordthe position of the spot of light exiting bonding tool 104. It is alsocontemplated that the PSD may be quad cell or bi-cell detector, asdesired.

In an exemplary embodiment, the focal point of the vision system(coincident with imaginary plane 211 shown in FIG. 2A) is located abovebottom surface 223 (shown in FIG. 2A) of cornercube 106. In addition,the exemplary embodiment includes two preferably identical lens elements108, 110 located at or below object plane 112A and image plane 112B.Another exemplary embodiment, shown in FIG. 2B, includes a single lenselement 205 located below plane 112 and in line with optical axes 114,116 (shown in FIG. 1). Hereinafter, the combination of cornercube 106(i.e., a cornercube prism), and lens elements 108, 110 (or lens element205) will be referred to as assembly 109, cornercube offset tool 109,and/or cornercube offset alignment tool 109.

The image plane of cornercube offset tool 109, including lens elements108, 110, is coincident with the object plane 112B of optical imagingunit 102. In other words, the image plane of cornercube 106 and lenselements 108, 110 are aligned to bonding tool 104 which also lies inobject plane 112A. In an exemplary embodiment, lens elements 108, 110(or 205) preferably have a unitary magnification factor. First lenselement 108 is positioned in a first optical axis 114 between bondingtool 104 and cornercube 106. Second lens element 110 is substantially inthe same plane as that of first lens element 108 and is positioned in asecond optical axis 116 between optical imaging unit 102 and cornercube106 (see FIG. 1). In one exemplary embodiment, first and second opticalaxes 114 and 116 are substantially parallel to one another, and arespaced apart from one another based on specific design considerations ofbonding machine 100. In one exemplary embodiment the distance 118between first optical axis 114 and second optical axis 116 is about0.400 in. (10.160 mm.) although distance 118 may be as small as about0.100 in. (2.54 mm) depending on design considerations related to thebonding machine.

FIG. 2A is a detailed side view of image ray traces and illustrates thegeneral imaging concept of an exemplary embodiment of the presentinvention. In FIG. 2A, exemplary ray traces 210, 214 are separated forclarity to illustrate the relative immunity of the resultant image dueto positional changes. The same distance also separates the image pointsbecause lens elements 108, 110 serve as unitary magnification relays.FIG. 2A also demonstrates how changes in the bonding tool 104 positionare compensated for. For example, once conventional methods have beenused to accurately measure the distance between imaging unit 102 andbonding tool 104 (shown in FIG. 1), the present invention is able tocompensate for changes in the bonding tool 104 offset position 222 dueto changes in the system. The location of bonding tool 104 can beaccurately measured because cornercube offset tool 109 images bondingtool 104 onto image plane 112B of the optical system (not shown in thisfigure).

The reference position of bonding tool 104 is shown as a reflected raywhich travels from first position 202 along first optical axis 114(shown in FIG. 1), as direct image ray bundle 210 from first position202 through first lens element 108. Direct image ray bundle 210continues along first optical axis 114 where it then passes through topsurface 226 of cornercube 106 onto first internal reflection surface218. Direct image ray bundle 210 is then reflected onto second internalreflection surface 220, which in turn directs it onto third internalreflective surface 221 (best shown in FIG. 3). Next, direct image raybundle 210 travels back through top surface 226 of cornercube 106 asreflected image ray bundle 212 along the second optical axis 116 (shownin FIG. 1) and through second lens element 110 to image plane 112B. Itis reflected image ray bundle 212 that is detected by imaging unit 102as image 204.

Consider now that the position of bonding tool 104 is displaced by adistance 222 due to a variation in system temperature, for example. Asshown in FIG. 2A, the displaced image of bonding tool 104 is shown asposition 206 and imaged along the path of second position ray trace 214.As shown in FIG. 2A, direct image ray bundle 214 travels along a pathsimilar to that of direct image ray bundle 210 from first position 202.Second position 206 image travels as a direct image ray bundle 214,through first lens element 108. Direct image ray bundle 214 then passesthrough top surface 226 of cornercube 106 onto first internal reflectionsurface 218. Direct image ray bundle 214 is then reflected onto secondinternal reflection surface 220, which in turn directs it onto thirdinternal reflection surface 221 (best shown in FIG. 3). Next, directimage ray bundle 214 travels through top surface 226 of cornercube 106as reflected image ray bundle 216 and through second lens element 110 toimage plane 112B. Reflected image ray bundle 216 is viewed as areflected image by imaging unit 102 as being in second position 208.Although the above example was described based on positional changesalong the X axis, it is equally applicable to changes along the Y axis.

As illustrated, the original displacement of bonding tool 104, shown asoffset position 222, is evidenced by the difference 224 in the measuredlocation of bonding tool 104 at second position 208 with respect toreference location 204. As evidenced by the above illustration, apositional shift in assembly 109 does not affect the reflected image asviewed by imaging unit 102. In other words, assembly 109 of the presentinvention may be translated along one or both the X and Y axes such thatthe image of the bonding tool 104 appears relatively stationary toimaging unit 102. There will be some minimal degree of error, however,in the measured position of bonding tool 104 due to distortion in thelens system (discussed in detail below).

Referring again to FIG. 2A, vertex 228 (shown in phantom) of cornercubeoffset alignment tool 109 is located at a position approximately midwaybetween first optical axis 114 and second optical axis 116. Tofacilitate mounting of cornercube 106, a lower portion 235 of cornercube106 may be removed providing bottom surface 223, which may besubstantially parallel to top surface 226. Removal of lower portion 235does not affect the reflection of image rays since the image raysemanating from object plane 112A do not impinge upon bottom surface 223.

Exemplary cornercube 106 comprises top surface 226, first reflectivesurface 218, bottom surface 223, second reflective surface 220, andthird reflective surface 221. If top surface 226 is set such thatoptical axes 114, 116 are normal to top surface 226, first reflectivesurface 218 will have a first angle 230 of about 45° relative to topsurface 226, and a second angle 234 of about 135° relative to bottomsurface 223. Likewise, ridgeline 225 (formed by the intersection ofsecond and third reflective surfaces 220 and 221) has similar angles 232and 236 relative to top surface 226 and bottom surface 223,respectively. In addition, second and third reflective surfaces 220 and221 are orthogonal to one another along ridgeline 225. In the exemplaryembodiment, bottom surface 223 of cornercube 106 may be used as amounting surface if desired. It should be noted, however, that it is notnecessary to form top surface 226 so that the image and reflected raysare normal thereto. As such, cornercube 106 will redirect the incidentlight or transmit image of bonding tool 104 parallel to itself with anoffset equal to 118.

The present invention can be used with light, for example, in thevisible, UV and IR spectrum, and preferably with light having awavelength that exhibits total internal reflection based on the materialfrom which cornercube 106 is fabricated. The material selected tofabricate cornercube offset alignment tool 109 is based on the desiredwavelength of light which the tool will pass. It is contemplated thatcornercube offset alignment tool 109 may be fabricated to handle apredetermined range of light wavelengths between the UV (1 nm) to thenear IR (3000 nm). In a preferred embodiment, the range of wavelength oflight may be selected from between about i) 1 and 400 nm, ii) 630 and690 nm, and iii) 750 and 3000 nm. Illumination may also be provided byambient light or by the use of an artificial light source (not shown).In one exemplary embodiment, typical optical glass, having an index ofrefraction of 1.5 to 1.7, may be used to fabricate cornercube 106. Note,the index of refraction is based upon the material chosen for maximumtransmission at the desired operating wavelength. In one embodiment,cornercube offset alignment tool 109 has an index of refraction of about1.517.

FIG. 3 is a perspective view of image ray traces according to anexemplary embodiment of the present invention translated in a directionperpendicular to the separation of lens elements 108, 110. The sameimage properties shown in FIG. 2A are also evident in FIG. 3. Forexample, the reference position of bonding tool 104 is represented byfirst position 302 and its image 304 is viewed as a first direct imageray 310 which travels along first optical axis 114 through first lenselement 108; passes through top surface 226 of cornercube 106; strikesfirst reflective surface 218 of cornercube 106; travels throughcornercube 106 in a path parallel to top surface 226; strikes secondreflective surface 220; strikes third reflective surface 221 beforeexiting the cornercube 106 through top surface 226 and travels alongsecond optical axis 116 through second lens element 110 onto image plane112B as ray traces 312 and viewed by imaging unit 102 at position 304.Positional displacement of bonding tool 104 is also shown in FIG. 3 andis illustrated by the path of the ray traces 314, 316 from secondposition 306 to second viewed position 308.

FIGS. 4A-4B are perspective and side views, respectively, of anexemplary embodiment of the present invention illustrating lens elements108, 110 and cornercube 106. The two lens elements 108, 110 (or 205) arepreferably doublets located above the cornercube 106 based on theirfocal distance from object plane 112A and image plane 112B, andimaginary plane 211. Doublets are preferred based on their superioroptical qualities. As illustrated in FIGS. 4A-4B, an exemplaryembodiment of cornercube 106 has three internal reflective surfaces,218, 220 and 221. As shown in FIG. 4B, the exterior edges of lenselements 108, 110 and cornercube 106 are coincident with one another.

FIG. 5 illustrates the telecentricity of an exemplary embodiment of theimage system of the present invention. As shown in FIG. 5, lens elements108, 110 produce a unitary magnification and are arranged relative tocornercube 106 such that the telecentricity of the machine vision systemis maintained. Note that front focal length 502 from lens element 108 tovertex 228 of cornercube 106 is equal to front focal length 502 fromlens element 110 to vertex 228 of cornercube 106. Note also, that backfocal length 504 from lens element 108 to object plane 112A is equal toback focal length 504 from lens element 110 to image plane 112B.

FIG. 6 is a detailed view of an exemplary cornercube 106 of the presentinvention. Note that internal reflection surface, 218 and ridgeline 225allow an image of bonding tool 104 to be translated in the X and Ydirections. Note also, that the surfaces of cornercube 106 arepreferably ground so that a reflected beam is parallel to the incidentbeam to within 5 arc seconds.

As shown in FIG. 6, surfaces 220 and 221 are orthogonal to one anotheralong ridgeline 225. In addition, the angle between ridgeline 225 andsurface 218 is about 90°. Furthermore, surface 218 and ridgeline form anangle of 45° relative to top surface 226 and bottom surface 223. Notealso, that surfaces, 218, 220, and 221 meet to form triangular shapedbottom surface 223, which may be used to facilitate mounting ofcornercube 106.

FIGS. 7A-7C illustrate the effect of tilt about the orthogonal axes ofcornercube offset alignment tool 109 in an exemplary vision system. FIG.7A is an overhead view of lens elements 108, 110 and cornercube 106.Exemplary image origins, 702, 703, 704, 706, 707 and 708 correspond topositions of image ray traces 210, 214 (shown in FIG. 2A). Note thatoptic axis position 710 corresponds to the position where the image ofbonding tool 104 (shown in FIG. 1) would be if cornercube 106 was nottilted along the Z axis.

FIGS. 7B-7C are graphs of the effect of tilt around the Z axis in termsof tilt in arc minutes vs. error in microns. FIG. 7B shows the effect oftilt around the Z axis versus error and image location along the Y axis.FIG. 7C shows the effect of tilt around the Z axis versus error andimage location along the X axis.

FIGS. 8A-8C illustrate the effect of tilt about the X and Y axis of theexemplary vision system. FIG. 8A is an additional side view of exemplaryimage ray traces 210, 212, 214, 216. In FIG. 8A, arrow 804 and dot 802are used to depict the X and Y axes, respectively, and arrow 806 depictstilt.

FIGS. 8B-8C are graphs of the effect of tilt around the X and Y axes interms of tilt in arc minutes vs. error in microns. FIG. 8B shows theeffect of tilt around the X axis versus error and image location alongthe Y axis. FIG. 8C shows the effect of tilt around the Y axis versuserror and image location along the X axis.

FIG. 9 is a detailed side view of image ray traces according to a thirdexemplary embodiment of the present invention. In FIG. 9, the referenceposition of bonding tool 104 is shown as a reflected ray which travelsfrom first position 914 (on object plane 112A which is part ofillustrated plane 112) along first optical axis 114 (shown in FIG. 1),as direct image ray bundle 922 from first position 914 through lenselement 902. Note that in this exemplary embodiment, lens element 902has a relatively planar, upper surface 904 and a convex lower surface906. Direct image ray bundle 922 continues along first optical axis 114where it then passes through upper surface 904 of lens element 902, andin turn through convex surface 906. Direct image ray bundle 922 is thenreflected onto total reflective surface 908. In a preferred embodiment,total reflective surface 908 is a mirror. Next, direct image ray bundle922 travels back through lens element 902 as reflected image ray bundle920 along second optical axis 116 (shown in FIG. 1) and onto image plane112B. It is reflected image ray bundle 920 that is detected by imagingunit 102 (shown in FIG. 1) as image 912. Similarly, positionaldisplacement of bonding tool 104 is also shown in FIG. 9 and isillustrated by the path of direct image ray bundles 918, 924 from secondposition 910 to second viewed position 916.

FIG. 14 illustrates an apparatus 1400 for measuring free air balls 1415used with a wire bonder (not shown in this figure) according to anexemplary embodiment of the present invention. As shown in FIG. 14,apparatus 1400 comprises optical imager 1402, such as imagers describedabove with respect to other exemplary embodiments, lenses 108, 110,cornercube offset tool 106, and illuminator 1220, such as a ringilluminator for example.

As shown in FIG. 14, lens 108 is positioned between object plane 1412and offset tool 106, while lens 110 is positioned between imager 1402and offset tool 106. In one non-limiting exemplary embodiment, lens 110and lens 108 are in the same horizontal plane. Desirably, apparatus 1400comprises both low and high magnifications as desired.

In use, free air ball 1415 is formed by an EFO system (not shown) at alower portion of capillary 1404. Imager 1402 is able to view free airball 1415 (from object plane 1412) as an image formed at image plane1410 via lens 108, cornercube offset tool 106 and lens 110.

The image of a free air ball 1415 is provided by optical imager 1402 toan image processing system (not shown in this figure) where dimensions,such as the diameter, of free air ball 1415 is determined. Based on thisdetermination the parameters of the EFO system may be adjusted in aclosed loop feed-back arrangement, as necessary, to control the diameterof further free air balls to continuously ensure proper bonding. Thus,the inventive controlled closed loop system may correct for anomalieswhich would otherwise cause free air ball 1415 to exceed its desireddiameter tolerance or to have a diameter too small during the wirebonding operation.

FIG. 15, illustrates an exemplary schematic block diagram of a closedloop system 1500. As shown in FIG. 15, an image 1501 of free air ball1405 is received by image system 1400. The image is provided by imagesystem 1400 to processor 1502, where the diameter of free air ball 1415is determined. Based on this determination a signal 1503 is provided toEFO system 1504 to adjust the parameters of EFO system 1504 so as toadjust the output 1506 of EFO system 1504, thus effecting the diameterof subsequent free air balls 1415.

Referring to FIG. 10A, a side view of yet another exemplary embodimentof the present invention is illustrated. In FIG. 10A, vision system 1000comprises multiple cornercube prisms 1014, 1020, 1026 and respectivelens sets 1016/1018, 1022/1024, 1028/1030, are used as an alignmentmeans to improve the accuracy of die attach and pick/place ofassemblies, such as die 1008, 1010, 1012. This will, in effect, replacea conventional up-looking camera (i.e., a die camera—not shown) found inmost conventional mid to high accuracy placement (e.g., die attach andpick/place) equipment. In the exemplary embodiment, ganged multiplecornercubes 1014, 1020, 1026 with varied lens separation distances,1017, 1023, 1029, respectively, provide an indirect image of a locationof die 1008, 1010, 1012, respectively. It is understood by those ofskill in the art that only one die is viewed at a time. The use ofmultiple cornercube/lens combinations allows for use with a variety ofdifferent sized die. In other respects, such as the materials used, themethod of reflection, etc., this exemplary embodiment is similar to thefirst exemplary embodiment.

As mentioned above, this variation of the first exemplary embodimentaccommodates various die sizes which these types of equipment accept andplace. In this exemplary embodiment, down looking optical detector 1002,such as a camera, (e.g., a substrate camera) views features on thedownward side of the component to be placed, such as die, 1008, 1010, or1012. These features of die 1008, 1010, 1012, can then be identified viaa vision system (not shown) to accurately place the die on the substrate(not shown) using pick tool 1004 based in part on the predetermineddistance 1006 between pick/place tool 1004 and optical detector 1002. Itis understood by those of skill in the art, that pick tool 1004 may beeither a rotating or non-rotating pick tool. This exemplary embodimentfurther preserves the optical advantages with respect to accuracy of thecornercube alignment described above in the first exemplary embodiment.

FIG. 10B is a plan view of the exemplary embodiment illustrated in FIG.10A. In FIG. 10B, cornercube prisms 1014, 1020, 1026 are placed adjacentone another to form assembly 1015. Cornercube prisms 1014, 1020, 1026may be bonded to one another, if desired using conventional adhesivemeans, or may be held in alignment with one another using a mechanicaldevice, such as a clamp or a containment assembly, for example. Thelatter approach allowing for simple replacement of individualcornercube/lens assemblies to accommodate different sized die, asdesired. Although the exemplary embodiment is shown with threecornercube offset tools, it is understood that at least two cornercubeoffset tools may be used.

Lenses 1016, 1018, 1022, 1024, 1028, 1030 may be formed from a unitaryoptical member rather than individual lenses if desired to simplifyassembly of the system. Such an approach is shown in FIGS. 10C-10D. Asshown in FIG. 10C, lens sheet 1040 has imbedded within optical members1016 a, 1018 a, 1022 a, 1024 a, 1028 a, 1030 a that are substantiallyequivalent to individual lenses 1016, 1018, 1022, 1024, 1028, 1030.

FIGS. 12A-12F illustrate further embodiments of the present invention.In these exemplary embodiments, a cornercube prism is used to improvethe accuracy of alignment of fibers. As in the previous exemplaryembodiment, the use of a cornercube prism allows for the use of a singleoptical detector instead of the conventional multiple detector systems.

Referring to FIG. 12A, the exemplary embodiment includes cornercubeprism 1014, lenses 1016, 1018, dark field illumination systems 1220,1221 (which are well known to those practicing the art) to illuminatethe fiber cladding edge 1210, 1211 of fiber cores 1212, 1213,respectively (which in turn produces reflections 1224, 1225 to outlinecladding edges 1210, 1211), and optical detector 1002. In this exemplaryembodiment, downward facing fiber 1208 is viewed by downward lookingoptical detector 1002, such as a camera (i.e., a substrate camera).Downward looking optical detector 1002 detects the emission of light1222 from fiber core 1212 and is then be able to determine the properoffset 1027 between the optical fiber centerline 1223 and central ray1229 of downward looking optical detector 1002. As is further shown inFIG. 12A, downward facing fiber 1208 and optical detector 1002 areoffset from one another by predetermined distance 1006. Also illustratedis upward facing fiber 1209 and associated dark field illuminationsystem 1221 positioned adjacent cornercube prism 1014.

FIG. 12B is a plan view of the exemplary embodiment illustrated in FIG.12A illustrating the relative positions of lenses set 1016/1018, andcornercube prism 1014.

In FIG. 12C, downward looking optical detector 1002 and downward facingfiber 1208 are then repositioned such that central ray 1229 of downwardlooking optical detector 1002 is aligned with fiber centerline 1231 ofupward facing fiber 1209. Once again, dark field illumination system1221 is used to illuminate upward facing fiber 1209 for recognition bythe vision system to ensure proper alignment with optical detector 1002.

Next, and as shown in FIG. 12D, optical detector 1002 and downwardfacing fiber 1208 are again repositioned based on the offset 1027determined during the process discussed above with respect to FIG. 12A.As a result, downward facing fiber 1208 and upward facing fiber 1209 arealigned with one another.

As shown in FIG. 12E, optical fibers 1208 and 1209 are then joined atjunction 1226 using conventional techniques, such as fusing the fiberstogether using radiation (not shown), or mechanical means, for example.

FIG. 12F illustrates yet a further embodiment of the present invention.In this exemplary embodiment, a cornercube offset alignment tool 1014 isused to align individual fibers (sub-fibers) 1202 a of a fiber opticsplitter 1200 with respective individual optical fibers 1208, etc. As inthe previous exemplary embodiment, the use of a cornercube offsetalignment tool allows for the use of a single optical detector insteadof the conventional multiple detector systems. As the steps leading upto alignment and coupling of optical fiber 1208 and sub-fiber 1202 a, b,etc., are similar to the above exemplary embodiment, they are notrepeated here.

Once the first sub-fiber is aligned with single fiber 1208, the processis repeated for a further sub-fiber, such as 1202 b, and another singlefiber (not shown).

Of course the exemplary embodiment is not limited to the fiber opticbundle of a fiber optic splitter being below optical detector 1002. Theembodiment also contemplates that the relative positions of fiber opticbundle 1200 and optical fiber 1208 are reversed, such that fiber opticbundle 1200 is positioned above cornercube prism 1014.

FIGS. 13A-13D illustrate a further embodiment of the present invention.In this exemplary embodiment, a cornercube offset alignment tool is usedto improve the accuracy of alignment of an optical fiber 1208 with acircuit element, such as a detector 1302. In FIG. 13A, exemplarydetector 1302 is part of an array 1300, although the invention is not solimited. It is also contemplated that detector 1302 may be a diode, suchas a photodiode or an emitter of optical radiation. As in the previousexemplary embodiments, the use of a cornercube offset alignment toolallows for the use of a single optical detector instead of theconventional multiple detector systems.

Referring to FIG. 13A, the exemplary embodiment includes cornercube1014, lenses 1016, 1018, dark field illumination system 1220 (which iswell known to those practicing the art) to illuminate the fiber claddingedge 1210 of fiber core 1212 (which in turn produces reflections 1024 tooutline cladding edge 1010), and optical detector 1002. In thisexemplary embodiment, downward facing fiber 1208 is viewed by downwardlooking optical detector 1002, such as a camera (e.g., a substratecamera). Downward looking optical detector 1002 detects the emission oflight 1222 from fiber core 1212 and is then able to determine the properoffset 1027 between the optical fiber centerline 1223 and central ray1229 of downward looking optical detector 1002. As is further shown inFIG. 13A, downward facing fiber 1208 and optical detector 1002 areoffset from one another by predetermined distance 1006.

In FIG. 13B, downward looking optical detector 1002 and downward facingfiber 1208 are then repositioned such that central ray 1229 of downwardlooking optical detector 1002 is aligned with optical centerline 1304 ofdetector 1302. It is understood that optical centerline 1304, may notnecessarily coincide with the physical center of detector 1302, butrather is dependent on the layout of the particular detector 1302. Inthis case the determination of optical centerline 1304 may beaccomplished by the location of the center of the active sensing area ofthe detector.

Next, and as shown in FIG. 13C, optical detector 1002 and downwardfacing fiber 1208 are again repositioned based on the offset 1027determined during the process discussed above with respect to FIG. 13A(offset 1027 is illustrated in FIG. 13A). As a result, downward facingfiber 1208 and detector 1302 are aligned with one another. As shown inFIG. 13D, optical fiber 1208 and detector 1302 are then kept in alignedposition using conventional techniques, such as optical epoxies, UVepoxies, for example.

Although the present invention has primarily been illustrated anddescribed with respect to a cornercube device (e.g., a cornercube prism)it is not limited thereto. Other prism devices may be used, particularlyother reflective prisms. In certain configurations of the presentinvention, it is desirable to have parallel image rays. In such aconfiguration, a reflective prism such as a cornercube prism may providea beam which enters and exits the prism substantially parallel to oneanother; however, in certain configurations non-parallel beams/imagerays may be desired, and other types of prisms may be utilized.

Although the present invention has primarily been described in relationto apparatuses and methods for measuring the size of a free air ball, itis not limited thereto. The apparatuses and methods disclosed herein areuseful for measuring a shape of a free air ball, a texture of a free airball, and any other quality of a free air ball that may be determinedusing the disclosed techniques. For example, such shapes and textures offree air balls may be compared to a threshold shape or texture tofurther control the free air ball formation process (e.g., a closed loopprocess).

Although the invention has been described with reference to exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed to include other variants and embodiments of theinvention, which may be made by those skilled in the art withoutdeparting from the true spirit and scope of the present invention.

1. A system for measuring the size of free air balls for use with a wirebonder having a wire bonding tool and an Electric Flame Off (EFO)device, the system comprising: an imager disposed above a first imageplane; a prism disposed below the imager; and at least one lenspositioned between the first image plane and the prism in a firstoptical path, the at least one lens positioned between the prism and theimager and in a second optical path, the second optical path beingdifferent from the first optical path, wherein an image of a free airball disposed at a lower portion of the wire bonding tool is provided tothe imager via the prism and the at least one lens, the imager beingpositioned at a height above a height of the free air ball, the prismbeing positioned at a height below the height of the free air ball, andthe at least one lens being positioned at a height between the height ofthe free air ball and the height of the prism.
 2. The system of claim 1wherein the prism is a cornercube prism.
 3. The system of claim 1wherein the at least one lens includes a first lens and a second lens,the first lens being positioned between the first image plane and theprism in the first optical path, and the second lens being positionedbetween the prism and the imager in the second optical path.
 4. Thesystem of claim 1 wherein the first optical path and the second opticalpath are substantially parallel to one another.
 5. The system accordingto claim 1, further comprising a processor in communication with theimager, the processor determining a size of the free air ball andproviding at least one control signal to the EFO device to control thesize of subsequent free air balls.
 6. The system of claim 1, furthercomprising a plurality of magnification levels.
 7. The system of claim1, further comprising an illuminator disposed adjacent the lower portionof the wire bonding tool.